The present invention relates to a sheet supply control apparatus and method for a printing press which supply sheet-like printing products to a printing unit one by one.
FIG. 6 shows the main part of an ink supply unit in the printing unit of a web offset printing press.
Referring to FIG. 6, an ink fountain 1 stores an ink 2. An ink fountain roller 3 supplies the ink 2 in the ink fountain 1 to an ink roller group 6. A plurality of ink fountain keys 4 are aligned in the axial direction of the ink fountain roller 3. An ink ductor roller 5 is arranged between the ink fountain roller 3 and ink roller group 6. A printing plate 7 is mounted on a plate cylinder 20.
In this ink supply unit, the ink 2 in the ink fountain 1 is supplied to the ink fountain roller 3 by adjusting the aperture ratios of the ink fountain keys 4. The ink 2 supplied to the ink fountain roller 3 is supplied to the printing plate 7 through the ink roller group 6 which is rotated in accordance with the feed operation of the ink ductor roller 5 in the operation of the printing press.
In the web offset printing press, when the printing plate is changed to a new printing plate 7, the aperture ratios of the ink fountain keys 4 and the rotation ratio of the ink fountain roller 3 are preset as preset data to values corresponding to the image of the printing plate 7. More specifically, the aperture ratios of the ink fountain keys 4 and the rotation ratio of the ink fountain roller 3 are set to values corresponding to the image of the new printing plate 7, and the ink 2 in the ink fountain 1 is supplied to the printing plate 7 through the ink roller group 6. In this case, test printing is performed before final printing to adjust the ink supply amount, thereby obtaining a satisfactory color tone. With this operation, a desired ink film thickness distribution (gradient of thickness of the ink film) is formed on the ink roller group 6.
In the conventional ink supply unit, however, when the printing plate is changed to the new printing plate 7 from the previous one, the ink film thickness distribution corresponding to the image on the previous printing plate remains on the ink roller group 6. For this reason, the ink film thickness distribution for the previous printing plate must be gradually changed to the ink film thickness distribution for the new printing plate 7. This operation excessively requires adjustment of the ink supply amount and test printing until a satisfactory color tone is obtained, resulting in various problems including an increase in preparation time for printing, an increase in work load, waste of printing materials, a decrease in production efficiency, and an increase in cost.
In order to decrease the numbers of operation times of adjustment of the ink supply amount and test printing that must be done until a satisfactory color tone is obtained, the present applicant/assignee proposed xe2x80x9cInk Film Thickness Control Method for Ink Supply Apparatusxe2x80x9d in U.S. Pat. Nos. 5,884,562 and 5,921,184. According to this ink film thickness control method, when the previous printing plate is to be exchanged to a new printing plate 7, an ink removing (deletion of ink history) operation is performed first.
In the ink removing operation, first, printing on a predetermined count of blank sheets is performed with the previous printing plate being mounted on the plate cylinder. In this case, after printing with the previous printing plate is completed, the blank sheet printing count is set, and the ink removing mode is selected on the operation panel. While the feed operation of an ink ductor roller 5 is stopped, the printing press is operated at a predetermined operation speed, and printing is performed for the preset blank sheet printing count.
At this time, on an ink roller group 6, a second ink film thickness distribution Mb (see FIG. 7B) corresponding to the image of the previous printing plate is superposed on a minimum first ink film thickness distribution Ma (see FIG. 7A) the thickness of which decreases from the upstream side to the downstream side and which is required during printing. When the feed operation of the ink ductor roller 5 is turned off and the printing press is operated with the previous printing plate being mounted, the ink on the ink roller group 6 is consumed, and its film thickness decreases gradually. In this case, the ink is consumed much on a zone having many images, and is consumed less on a zone having few images. After printing is performed for the preset blank sheet printing count, the first ink film thickness distribution Ma is left on the ink roller group 6.
In this case, the blank sheet printing count which is preset for ink removing can be obtained from preset data for final data of the previous printing plate. More specifically, an ink supply amount is obtained from the preset data for final printing, and the second ink film thickness distribution Mb left on the ink roller group 6 is obtained from the obtained ink supply amount. The relationship between the second ink film thickness distribution Mb and the blank sheet printing count is obtained through tests in advance in the form of a table. Therefore, when the table data is looked up with reference to the obtained second ink film thickness distribution Mb, the blank sheet printing count necessary for leaving the first ink film thickness distribution Ma can be obtained. The obtained blank sheet printing count can be freely set or changed by the operator through a ten-key pad and the like.
In this manner, ink removing is ended with the first ink film thickness distribution Ma left on the ink roller group 6. After ink removing, the operator cleans the blanket, and changes the previous printing plate to the new printing plate 7.
In the web offset printing plate described above, sheets are supplied to the printing unit for ink removing as shown in FIG. 8. Referring to FIG. 8, a sheet detector 9 is set at a terminal end (front lay) 8a of a feeder board 8 to detect sheets 11 attracted by a sucker 10 and supplied onto the feeder board 8 one by one. In this case, after the first sheet 11 is detected, every time the sheet 11 is supplied, a pulse (timing pulse of the printing press) generated by a pulse generator (rotary encoder) is counted. When the number of pulses becomes equal to the preset blank sheet printing count, the sheet supply operation of the sucker 10 is stopped, and the operation of the printing press is stopped.
Therefore, in the conventional case, after printing for the preset blank sheet count is performed, a sheet 11 remains on the feeder board 8 between the sucker 10 and sheet detector 9. This sheet 11 must be removed, posing a load to the operator. The removed sheet 11 is discarded, which is a waste.
It is an object of the present invention to provide a sheet supply control apparatus and method for a printing press, in which, after printing for a preset printing count is performed, an operation of removing a sheet on a supply path to a printing unit need not be performed.
In order to achieve the above object, according to the present invention, there is provided a sheet supply control apparatus for a printing press, comprising sheet supply means for supplying sheet-like objects to a printing unit one by one with a predetermined supply interval, setting means in which a count of sheet-like objects to be supplied to the printing unit is set, detection means for detecting the sheet-like objects supplied from the sheet supply means, count means for counting sheet-like objects supplied from the sheet supply means after the detection means detects a first sheet-like object, and sheet supply control means for controlling supply operation of the sheet supply means, on the basis of the count preset in the setting means and the count of the count means, such that the count of sheet-like objects supplied from the sheet supply means coincides with the count preset in the setting means.